1. Field of the Invention
This invention relates to a brain wave inducing apparatus for inducing brain waves such as .alpha., .beta., and .theta. waves from a human body through optical stimulation.
2. Related Art
It is well known that there is a close relationship between the brain waves of a person and his or her biological, psychological conditions. For example, .alpha. waves (about 8-13 Hz) are dominantly developed when a person is relaxed, .beta. waves (about 14-30 Hz) are dominant when mentally and physically active, and .theta. waves (about 4-7 Hz) are dominant when the person is sleepy.
Conversely, if a specific brain wave is induced dominantly, then the person will enter the corresponding physical and psychological condition. Therefore, the use of the relationship between these brain waves and their corresponding physical, psychological conditions may be useful in controlling physical and psychological conditions in human beings.
Laid Open Japanese Patent Publication No. 62-87165 discloses a "relaxing apparatus." With this apparatus, a white noise outputted from a random signal generator is directed to a filter having a 1/f characteristic that produces a fluctuation signal of 1/f characteristic. A reference frequency set within the .alpha. frequency range (about 8-13 Hz) is frequency-modulated by the fluctuation signal. This frequency-modulated signal Vp drives a light emitting device to cycle on and off so as to produce a stimulating light whose time interval fluctuates with 1/f characteristic. Thereby, this stimulating signal is used to induce .alpha. waves in a patient. The frequency modulated signal Vp has a constant amplitude and a regular waveform.
.alpha. waves as well as other brain waves, are usually not uniform in waveform and amplitude. It is known that brain waves have a so-called "pull-in phenomenon" where a specific brain wave is "pulled in" or induced in response to an optical stimulation. When effectively inducing a specific brain wave by using the pull-in phenomenon, an optically stimulating signal should have a waveform as close to an actual brain wave as possible. From this point of view, the waveform of the frequency-modulated signal Vp of the relax apparatus disclosed by Laid Open Japanese Patent No. 62-87165 is too simple and not satisfactory. Thus, the use of the brain wave of a patient is the most efficient way of inducing a desired brain wave from that patient. However, picking up the brain waves from the patient will usually require electrodes and cords as well as many accessory circuits such as signal processing circuits, which makes the apparatus complex, large and burdensome.